<!DOCTYPE html>
<html lang="zh-Hans">
<head>
  <meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2">
<meta name="theme-color" content="#222">
<meta name="generator" content="Hexo 5.3.0">
  <link rel="apple-touch-icon" sizes="180x180" href="/blog/images/apple-touch-icon-next.png">
  <link rel="icon" type="image/png" sizes="32x32" href="/blog/images/favicon-32x32-next.png">
  <link rel="icon" type="image/png" sizes="16x16" href="/blog/images/favicon-16x16-next.png">
  <link rel="mask-icon" href="/blog/images/logo.svg" color="#222">

<link rel="stylesheet" href="/blog/css/main.css">

<link rel="stylesheet" href="//fonts.googleapis.com/css?family=Lato:300,300italic,400,400italic,700,700italic&display=swap&subset=latin,latin-ext">
<link rel="stylesheet" href="/blog/lib/font-awesome/css/font-awesome.min.css">


<script id="hexo-configurations">
  var NexT = window.NexT || {};
  var CONFIG = {
    hostname: new URL('https://guodh.gitee.io/blog').hostname,
    root: '/blog/',
    scheme: 'Pisces',
    version: '7.7.1',
    exturl: false,
    sidebar: {"position":"left","display":"post","padding":18,"offset":12,"onmobile":false},
    copycode: {"enable":true,"show_result":true,"style":null},
    back2top: {"enable":true,"sidebar":false,"scrollpercent":false},
    bookmark: {"enable":false,"color":"#222","save":"auto"},
    fancybox: false,
    mediumzoom: false,
    lazyload: false,
    pangu: false,
    comments: {"style":"tabs","active":null,"storage":true,"lazyload":false,"nav":null},
    algolia: {
      appID: '',
      apiKey: '',
      indexName: '',
      hits: {"per_page":10},
      labels: {"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}
    },
    localsearch: {"enable":false,"trigger":"auto","top_n_per_article":1,"unescape":false,"preload":false},
    path: 'search.xml',
    motion: {"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}}
  };
</script>

  <meta name="description" content="最近在写业务代码的时候用到的SETNX，但是在牛肉的提醒下才发现我对SETNX的理解有很多的问题，果然还是NO BI BI, SHOW ME THE CODE比较实际。 SETNX先讲下原理：SETNX提供了一个锁的概念，通过判断返回值（0或者1）来执行不同的逻辑，包含了GET和SET的逻辑，在原来GET或者SET的场景直接使用SETNX就好。通过使用SETNX能够应用于业务去重，以及防止缓存穿透">
<meta property="og:type" content="article">
<meta property="og:title" content="Jedis实践">
<meta property="og:url" content="https://guodh.gitee.io/blog/2017/02/22/2017/jedis%E5%AE%9E%E8%B7%B5/index.html">
<meta property="og:site_name" content="蛋蛋的小屋">
<meta property="og:description" content="最近在写业务代码的时候用到的SETNX，但是在牛肉的提醒下才发现我对SETNX的理解有很多的问题，果然还是NO BI BI, SHOW ME THE CODE比较实际。 SETNX先讲下原理：SETNX提供了一个锁的概念，通过判断返回值（0或者1）来执行不同的逻辑，包含了GET和SET的逻辑，在原来GET或者SET的场景直接使用SETNX就好。通过使用SETNX能够应用于业务去重，以及防止缓存穿透">
<meta property="og:locale">
<meta property="article:published_time" content="2017-02-22T10:36:55.000Z">
<meta property="article:modified_time" content="2017-10-02T03:13:21.000Z">
<meta property="article:author" content="RunningEgg">
<meta property="article:tag" content="技术">
<meta name="twitter:card" content="summary">

<link rel="canonical" href="https://guodh.gitee.io/blog/2017/02/22/2017/jedis%E5%AE%9E%E8%B7%B5/">


<script id="page-configurations">
  // https://hexo.io/docs/variables.html
  CONFIG.page = {
    sidebar: "",
    isHome: false,
    isPost: true
  };
</script>

  <title>Jedis实践 | 蛋蛋的小屋</title>
  






  <noscript>
  <style>
  .use-motion .brand,
  .use-motion .menu-item,
  .sidebar-inner,
  .use-motion .post-block,
  .use-motion .pagination,
  .use-motion .comments,
  .use-motion .post-header,
  .use-motion .post-body,
  .use-motion .collection-header { opacity: initial; }

  .use-motion .site-title,
  .use-motion .site-subtitle {
    opacity: initial;
    top: initial;
  }

  .use-motion .logo-line-before i { left: initial; }
  .use-motion .logo-line-after i { right: initial; }
  </style>
</noscript>

</head>

<body itemscope itemtype="http://schema.org/WebPage">
  <div class="container use-motion">
    <div class="headband"></div>

    <header class="header" itemscope itemtype="http://schema.org/WPHeader">
      <div class="header-inner"><div class="site-brand-container">
  <div class="site-meta">

    <div>
      <a href="/blog/" class="brand" rel="start">
        <span class="logo-line-before"><i></i></span>
        <span class="site-title">蛋蛋的小屋</span>
        <span class="logo-line-after"><i></i></span>
      </a>
    </div>
        <p class="site-subtitle">来了就看看吧，没有刀剑只有故事</p>
  </div>

  <div class="site-nav-toggle">
    <div class="toggle" aria-label="Toggle navigation bar">
      <span class="toggle-line toggle-line-first"></span>
      <span class="toggle-line toggle-line-middle"></span>
      <span class="toggle-line toggle-line-last"></span>
    </div>
  </div>
</div>


<nav class="site-nav">
  
  <ul id="menu" class="menu">
        <li class="menu-item menu-item-home">

    <a href="/blog/" rel="section"><i class="fa fa-fw fa-home"></i>Home</a>

  </li>
        <li class="menu-item menu-item-about">

    <a href="/blog/about/" rel="section"><i class="fa fa-fw fa-user"></i>About</a>

  </li>
        <li class="menu-item menu-item-archives">

    <a href="/blog/archives/" rel="section"><i class="fa fa-fw fa-archive"></i>Archives</a>

  </li>
        <li class="menu-item menu-item-book">

    <a href="/blog/book/" rel="section"><i class="fa fa-fw fa-archive"></i>book</a>

  </li>
  </ul>

</nav>
</div>
    </header>

    
  <div class="back-to-top">
    <i class="fa fa-arrow-up"></i>
    <span>0%</span>
  </div>


    <main class="main">
      <div class="main-inner">
        <div class="content-wrap">
          

          <div class="content">
            

  <div class="posts-expand">
      
  
  
  <article itemscope itemtype="http://schema.org/Article" class="post-block " lang="zh-Hans">
    <link itemprop="mainEntityOfPage" href="https://guodh.gitee.io/blog/2017/02/22/2017/jedis%E5%AE%9E%E8%B7%B5/">

    <span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
      <meta itemprop="image" content="/blog/images/avatar.gif">
      <meta itemprop="name" content="RunningEgg">
      <meta itemprop="description" content="写下我的点点滴滴，写下我对这个世界的看法，还有我内心锁崇拜的技术">
    </span>

    <span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
      <meta itemprop="name" content="蛋蛋的小屋">
    </span>
      <header class="post-header">
        <h1 class="post-title" itemprop="name headline">
          Jedis实践
        </h1>

        <div class="post-meta">
            <span class="post-meta-item">
              <span class="post-meta-item-icon">
                <i class="fa fa-calendar-o"></i>
              </span>
              <span class="post-meta-item-text">Posted on</span>

              <time title="Created: 2017-02-22 18:36:55" itemprop="dateCreated datePublished" datetime="2017-02-22T18:36:55+08:00">2017-02-22</time>
            </span>
              <span class="post-meta-item">
                <span class="post-meta-item-icon">
                  <i class="fa fa-calendar-check-o"></i>
                </span>
                <span class="post-meta-item-text">Edited on</span>
                <time title="Modified: 2017-10-02 11:13:21" itemprop="dateModified" datetime="2017-10-02T11:13:21+08:00">2017-10-02</time>
              </span>

          

        </div>
      </header>

    
    
    
    <div class="post-body" itemprop="articleBody">

      
        <p>最近在写业务代码的时候用到的SETNX，但是在牛肉的提醒下才发现我对SETNX的理解有很多的问题，果然还是NO BI BI, SHOW ME THE CODE比较实际。</p>
<h3 id="SETNX"><a href="#SETNX" class="headerlink" title="SETNX"></a>SETNX</h3><p>先讲下原理：<br>SETNX提供了一个锁的概念，通过判断返回值（0或者1）来执行不同的逻辑，包含了GET和SET的逻辑，在原来GET或者SET的场景直接使用SETNX就好。通过使用SETNX能够应用于业务去重，以及防止缓存穿透等场景。<br>一般做法：在更新缓存前，先判断SETNX是否存在，保证只有一个线程进入update（获得资源），其余的线程则是等待或者读取以前缓存的数据。</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// redis提供的setnx没有过期时间，从2.6.12之后set涵盖setnx功能，提供过期</span></span><br><span class="line"><span class="comment">// String statusCode = redis.set(&quot;lock&quot;, value, &quot;NX&quot;, &quot;EX&quot;, expire); 和下面使用setnx相同</span></span><br><span class="line">String statusCode = redis.setnx(<span class="string">&quot;lock&quot;</span>, value);</span><br><span class="line"><span class="keyword">if</span>( <span class="string">&quot;OK&quot;</span> == statusCode) &#123;</span><br><span class="line">  <span class="comment">// 成功获得锁，更新数据场景</span></span><br><span class="line">  db.select(....);</span><br><span class="line">  <span class="comment">// 这里可能比较耗时，例如200ms</span></span><br><span class="line">  redis.update();</span><br><span class="line">  redis.del(key);</span><br><span class="line">&#125; <span class="keyword">else</span> &#123;</span><br><span class="line">  <span class="comment">// 没有获得锁，使用过期数据场景</span></span><br><span class="line">  redis.get(); <span class="comment">// or 或者一直等待</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>这里需要像类似我这种小白的人，说明的是Redis是单线程的，提供一个队列模型，能够保证有序的执行每个command。同时，通过各种资料查的Redis的SET和GET都是原子性的（实验方法：SET1到1000，同时GET，发现数据并没有影响）。<br>但是在SETNX和Del之间，会执行业务逻辑，业务逻辑并不是原子性的，在这段时间内Redis还会有多个GET。这部分数据会在大并发的时候，造成缓存穿透，有可能导致DB挂掉。<br>start-&gt; SETNX -&gt; GET -&gt; GET -&gt; …. -&gt;Get-&gt;Del -&gt; end<br>Get 的长度取决于业务逻辑执行时间。</p>
<p>SETNX只是提供了一个锁的概念，并不是存储数据（我一直以为SETNX是用来存数据的……尴尬）<br>参考: <a href="http://huoding.com/2015/09/14/463">http://huoding.com/2015/09/14/463</a></p>
<h3 id="Jedis源码"><a href="#Jedis源码" class="headerlink" title="Jedis源码"></a>Jedis源码</h3><p>在排查的过程中，顺便看了下Jedis的源码，这里也一并记录下来希望对人有帮助</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">protected</span> Connection <span class="title">sendCommand</span><span class="params">(<span class="keyword">final</span> Command cmd, <span class="keyword">final</span> <span class="keyword">byte</span>[]... args)</span> </span>&#123;</span><br><span class="line">    <span class="keyword">try</span> &#123;</span><br><span class="line">      connect();</span><br><span class="line">      Protocol.sendCommand(outputStream, cmd, args);</span><br><span class="line">      pipelinedCommands++;</span><br><span class="line">      <span class="keyword">return</span> <span class="keyword">this</span>;</span><br><span class="line">    &#125; <span class="keyword">catch</span> (JedisConnectionException ex) &#123;</span><br><span class="line">      <span class="comment">/**发送有问题数据，会返回errorMessage*/</span></span><br><span class="line">      <span class="keyword">try</span> &#123;</span><br><span class="line">        String errorMessage = Protocol.readErrorLineIfPossible(inputStream);</span><br><span class="line">        <span class="keyword">if</span> (errorMessage != <span class="keyword">null</span> &amp;&amp; errorMessage.length() &gt; <span class="number">0</span>) &#123;</span><br><span class="line">          ex = <span class="keyword">new</span> JedisConnectionException(errorMessage, ex.getCause());</span><br><span class="line">        &#125;</span><br><span class="line">      &#125; <span class="keyword">catch</span> (Exception e) &#123;</span><br><span class="line">      broken = <span class="keyword">true</span>;</span><br><span class="line">      <span class="keyword">throw</span> ex;</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br></pre></td></tr></table></figure>
<p>可以看到jedis先把args塞到command中，然后把command放到Protocal的队列中</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">sendCommand</span><span class="params">(<span class="keyword">final</span> RedisOutputStream os, <span class="keyword">final</span> <span class="keyword">byte</span>[] command,</span></span></span><br><span class="line"><span class="function"><span class="params">      <span class="keyword">final</span> <span class="keyword">byte</span>[]... args)</span> </span>&#123;</span><br><span class="line">    <span class="keyword">try</span> &#123;</span><br><span class="line">      os.write(ASTERISK_BYTE);</span><br><span class="line">      os.writeIntCrLf(args.length + <span class="number">1</span>);</span><br><span class="line">      os.write(DOLLAR_BYTE);</span><br><span class="line">      os.writeIntCrLf(command.length);</span><br><span class="line">      os.write(command);</span><br><span class="line">      os.writeCrLf(); <span class="comment">// --&gt;作用是flushBuffer,立刻将缓存的数据写入预期目标</span></span><br><span class="line"></span><br><span class="line">      <span class="keyword">for</span> (<span class="keyword">final</span> <span class="keyword">byte</span>[] arg : args) &#123;</span><br><span class="line">        os.write(DOLLAR_BYTE);</span><br><span class="line">        os.writeIntCrLf(arg.length);</span><br><span class="line">        os.write(arg);</span><br><span class="line">        os.writeCrLf(); <span class="comment">// --&gt;作用是flushBuffer</span></span><br><span class="line">      &#125;</span><br><span class="line">    &#125; <span class="keyword">catch</span> (IOException e) &#123;</span><br><span class="line">      <span class="keyword">throw</span> <span class="keyword">new</span> JedisConnectionException(e);</span><br><span class="line">    &#125;</span><br><span class="line">  &#125;</span><br></pre></td></tr></table></figure>
    </div>

    
    
    

      <footer class="post-footer">
          <div class="post-tags">
              <a href="/blog/tags/%E6%8A%80%E6%9C%AF/" rel="tag"># 技术</a>
          </div>

        


        
    <div class="post-nav">
      <div class="post-nav-item">
    <a href="/blog/2017/02/22/2017/%E6%A1%86%E6%9E%B6%E7%9A%84%E4%BB%B7%E5%80%BC/" rel="prev" title="框架的价值">
      <i class="fa fa-chevron-left"></i> 框架的价值
    </a></div>
      <div class="post-nav-item">
    <a href="/blog/2017/02/25/2017/Executor%E5%8E%9F%E7%90%86%E5%88%86%E6%9E%90/" rel="next" title="Executor原理分析">
      Executor原理分析 <i class="fa fa-chevron-right"></i>
    </a></div>
    </div>
      </footer>
    
  </article>
  
  
  

  </div>


          </div>
          

<script>
  window.addEventListener('tabs:register', () => {
    let activeClass = CONFIG.comments.activeClass;
    if (CONFIG.comments.storage) {
      activeClass = localStorage.getItem('comments_active') || activeClass;
    }
    if (activeClass) {
      let activeTab = document.querySelector(`a[href="#comment-${activeClass}"]`);
      if (activeTab) {
        activeTab.click();
      }
    }
  });
  if (CONFIG.comments.storage) {
    window.addEventListener('tabs:click', event => {
      if (!event.target.matches('.tabs-comment .tab-content .tab-pane')) return;
      let commentClass = event.target.classList[1];
      localStorage.setItem('comments_active', commentClass);
    });
  }
</script>

        </div>
          
  
  <div class="toggle sidebar-toggle">
    <span class="toggle-line toggle-line-first"></span>
    <span class="toggle-line toggle-line-middle"></span>
    <span class="toggle-line toggle-line-last"></span>
  </div>

  <aside class="sidebar">
    <div class="sidebar-inner">

      <ul class="sidebar-nav motion-element">
        <li class="sidebar-nav-toc">
          Table of Contents
        </li>
        <li class="sidebar-nav-overview">
          Overview
        </li>
      </ul>

      <!--noindex-->
      <div class="post-toc-wrap sidebar-panel">
          <div class="post-toc motion-element"><ol class="nav"><li class="nav-item nav-level-3"><a class="nav-link" href="#SETNX"><span class="nav-number">1.</span> <span class="nav-text">SETNX</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#Jedis%E6%BA%90%E7%A0%81"><span class="nav-number">2.</span> <span class="nav-text">Jedis源码</span></a></li></ol></div>
      </div>
      <!--/noindex-->

      <div class="site-overview-wrap sidebar-panel">
        <div class="site-author motion-element" itemprop="author" itemscope itemtype="http://schema.org/Person">
  <p class="site-author-name" itemprop="name">RunningEgg</p>
  <div class="site-description" itemprop="description">写下我的点点滴滴，写下我对这个世界的看法，还有我内心锁崇拜的技术</div>
</div>
<div class="site-state-wrap motion-element">
  <nav class="site-state">
      <div class="site-state-item site-state-posts">
          <a href="/blog/archives/">
        
          <span class="site-state-item-count">89</span>
          <span class="site-state-item-name">posts</span>
        </a>
      </div>
      <div class="site-state-item site-state-tags">
        <span class="site-state-item-count">24</span>
        <span class="site-state-item-name">tags</span>
      </div>
  </nav>
</div>
  <div class="links-of-author motion-element">
      <span class="links-of-author-item">
        <a href="mailto:guodh_1@163.com" title="E-Mail → mailto:guodh_1@163.com" rel="noopener" target="_blank"><i class="fa fa-fw fa-envelope"></i>E-Mail</a>
      </span>
  </div>



      </div>

    </div>
  </aside>
  <div id="sidebar-dimmer"></div>


      </div>
    </main>

    <footer class="footer">
      <div class="footer-inner">
        

<div class="copyright">
  
  &copy; 
  <span itemprop="copyrightYear">2022</span>
  <span class="with-love">
    <i class="fa fa-user"></i>
  </span>
  <span class="author" itemprop="copyrightHolder">RunningEgg</span>
</div>
  <div class="powered-by">Powered by <a href="https://hexo.io/" class="theme-link" rel="noopener" target="_blank">Hexo</a> v5.3.0
  </div>
  <span class="post-meta-divider">|</span>
  <div class="theme-info">Theme – <a href="https://pisces.theme-next.org/" class="theme-link" rel="noopener" target="_blank">NexT.Pisces</a> v7.7.1
  </div>

        








      </div>
    </footer>
  </div>

  
  <script src="/blog/lib/anime.min.js"></script>
  <script src="/blog/lib/velocity/velocity.min.js"></script>
  <script src="/blog/lib/velocity/velocity.ui.min.js"></script>

<script src="/blog/js/utils.js"></script>

<script src="/blog/js/motion.js"></script>


<script src="/blog/js/schemes/pisces.js"></script>


<script src="/blog/js/next-boot.js"></script>




  















  

  

</body>
</html>
